The present invention relates to a spindle device for use in a machine tool, and more particularly, to a type thereof in which an improvement is made on lifting and suspending a tool detachably secured thereto.
In a conventional spindle device for use in a machine tool, a drawbar provided in the spindle unit is moved to a direction opposite a tool attaching direction by way of a force which is generated when a biasing means such as a belleville spring is compressed. In response to this movement of the drawbar, a tool holding member provided at a tip end portion of the drawbar is closed for lockingly supporting the tool. Further, the tool is fixedly secured to the spindle by pulling up a pullstud of the tool by the drawbar.
On the other hand, for detaching the tool from the spindle, a rear end portion of the drawbar is depressed by a depression means such as a hydraulic cylinder, so that the drawbar is moved toward the tool against the biasing force of the biasing means. By this movement, the tool holding member is opened for releasing the pullstud, whereby the tool is detachable from the spindle.
With such conventional arrangement, sufficiently large biasing force of the biasing means is required, for example, about 1000 kgf in BT40 scale, in order to securely hold the tool. For this purpose, the biasing means must provide large biasing force. Accordingly, in the conventional spindle device, large force is required for changing an assembled tool for a new tool. Further, due to exertion of large biasing force, large thrusting load is imparted on a bearing, to lower a service life thereof.
If a belleville spring is used as the biasing means, the spring may be displaced from a rotation center of the spindle when the latter is rotated at high speed, to thereby provide operational imbalance. On the other hand, if a coil spring is used for the biasing means, the resultant spindle becomes bulky, since a mass of the coil spring is larger than that of the belleville spring.